Why is self-discipline a by-product of the Montessori method?

The amount of self-direction allowed by the integrated approach described above leads children to a natural love of learning. From an early age, they understand that they are responsible for the quality of their work. When a child's mind is "sensitive" to a particular interest, the topic's incremental parts begin to make "sense" to the child, and tremendous satisfaction and joy comes from exploring it fully.